Most computer users employ some sort of data protection procedures and devices to protect computer system files and data files in the event of an accidental delete, corruption or overwrite of these files from the primary storage medium, or the failure or loss of the storage medium, which is usually the computer's hard drive. Computer data protection systems usually involve the backup of system and data files onto some sort of secondary storage device utilizing removable storage media, such as floppy disk drives, other hard disk drives, tape drives, etc. More sophisticated users may utilize automatic data protection devices and procedures that backup the entire system on a regular basis, allowing for a full system recovery if needed.
For example, tape backup systems are used to protect data files and other information from computer system failures such as hard disk crashes or computer virus attacks. A tape backup system stores this data on removable off-line media (i.e., the tape); this data can then be retrieved in the event of data loss. Conventional backup systems typically provide the end user with a choice of making a “full” backup or an “incremental” or “modified” backup. Full backups make complete copies of all the data on the computer to a set of one or more backup tapes. Incremental backups are generally much smaller than full backups since they simply save the data that has been changed since either the last full backup or the most recent incremental backup. Examples of such prior art backup systems are described in U.S. Pat. No. 5,276,860, U.S. Pat. No. 5,758,067, U.S. Pat. No. 6,212,512, U.S. Pat. No. 6,330,570 and WO 01/31431 A2.
FIG. 1 shows a block diagram of a prior art computer system which enables interleaved backups. Host computers 10, 12, 14 are coupled to backup server computer 16 by means of network 18. For example network 18 is a local area network (LAN). Backup server computer 16 is coupled to tape drive 20 by means of storage area network (SAN) 22.
In operation the backup server computer 16 communicates with the host computers 10, 12 and 14 over network 18 in order to pull the backup data from the host computers 10, 12 and 14. The backup server computer interleaves the respective data streams received from host computers 10, 12 and 14 before sending the single interleaved data stream to tape drive 20 via storage area network 22.
This approach has the primary disadvantage that backup server computer 16 serves as a central hub for the entire backup process. This implies that the backup server computer must be capable of handling the high data rates of the backup data from the host computers at both its inputs and its output. Further this requires sophisticated backup software and makes restoring the data dependent on that particular interleaving capability.
Another disadvantage is that the streaming of the backup data from the host computers to the backup server computer over the network 18 may saturate the transmission capacity of the network 18. This is a severe problem as network 18 is often a production network that is required for ongoing operational activities and is not optimised for storage activities.
An example of a technology that may be used for backup is the linear tape-open (LTO) technology. LTO technology is an “open format” technology, which means that users can have multiple sources of media and compatible tape drives. The ULTRIUM format is the “high capacity” implementation of LTO technology.
Tape drives and tape cartridges which are compliant with ULTRIUM LTO are commercially available from Hewlett Packard and others. A LTO compliant cartridge has a non-volatile cartridge memory (LTO-CM) which is an intelligent memory chip embedded in the cartridge. It uses a radio frequency interface that eliminates the need for a physical power or signal connection between cartridge and tape drive. The LTO-CM is used for storing information which in other tape formats may be stored in the header at the beginning of the tape.